BIG PHYSICS, BIG QUESTIONS –

Fog catchers pull water from air in Chile’s dry fields

Just south of the Atacama desert, prototype fog catchers are watering Chilean farms struggling with drought and climate change

By Aleszu Bajak

Pulling water out of thin air

(Image: Isifa Image Service s.r.o./Alamy)

WHERE the cold waters of the Humboldt current meet the dry hot air along northern Chile, a thick fog rises up off the Pacific and is blown inland over the arid coast. On these barren steppes just south of the Atacama desert lies a lush forest where trees suck moisture from the fog.

A new team from Chile and the Massachusetts Institute of Technology is mimicking these natural fog catchers to provide water for drinking and crop irrigation in this parched region.

Water scarcity is a serious problem near the small city of Ovalle where smallholder farmers grow grapes, avocados and artichokes. Dwindling reservoirs and falling water tables have forced the region’s agricultural communities to ration water. That’s where fog-catching technology could help.

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Fog on its way?

(Image: K-C.Park)

In November, a team of engineers and a geographer climbed a hillside near Ovalle to install what looks like a small square billboard (see photo). Stretched taut between two posts is a metre-square stainless steel mesh above a gutter that empties out into a plastic drum. Similar prototypes allow gravity to feed the collected water into irrigation ponds. Farmers in this part of Chile have already used fog-harvested water to irrigate their crops. Scaled up, they could help people in the area battle the effects of climate change.

But catching fog with mesh is no simple task. If too much water is trapped inside the fibres, the mesh won’t drain, like a waterlogged pair of jeans. If the holes are too large, wind will blow the droplets through. Mesh clogging and droplet blow-through hinder the efficiency of the typical mesh used in more basic fog catchers. Various fog catchers have been in use for decades, but the new design takes them to another level, says MIT’s Gareth McKinley.

“Our coated mesh was five times as efficient at collecting fog as the mesh currently used,” McKinley says. He and his colleagues optimised the mesh hole size and hydrophobic coating to maximise the efficiency of their device’s fog collection. Fog catchers generally catch less than 5 litres of water per square metre of mesh per day, depending on wind speed and the water content of the fog as well as other factors. McKinley’s design captured 12 litres per square metre per day.

Richard LeBoeuf and his students at the University of Los Andes in Chile’s capital Santiago have designed a probe that can measure the moisture content and velocity of the fog in hopes of inferring its prevailing direction. They linked a series of these probes to a laptop and beamed the data over broadband wireless back to LeBoeuf’s office 400 kilometres away. The networked probe system, dubbed FogFinder, was a finalist in Vodaphone’s 2014 Wireless Innovation competition last month.

The next step would be to fit the fog catchers with mechanisms that let them spin in the wind, like turbines.”We are trying to move out of the artisanal phase and into the industrial phase,” says team member Pilar Cereceda, a geographer at the Pontifical Catholic University of Chile, who has been studying site selection for decades, and drumming up local interest in fog catchers.

Cereceda’s group and others – like a Canadian company called FogQuest – have set up prototypes across northern Chile. Most employ the Raschel net, which is less efficient than the new material. Similar projects have been providing water for local people in Nepal, Guatemala, Morocco and Ethiopia.

With the right government incentives, the technology could take off, says Cereceda.

“You could imagine fog catchers like wind farms, 20 or 100 of them up on a hillside,” agrees McKinley. “Anywhere you can build a billboard or a cell tower on a hillside, you should build a fog catcher. They’re modular, they’re scalable and you don’t need to plug them into the grid. Nature does all the work.”

Anywhere you can build a billboard or a cell tower on a hillside, you should build a fog catcher

This article appeared in print under the headline “Catcher in the fog”